Typical cleaning systems for ink jet printers include separate cleaning elements for each color of ink employed by the printer. The motivation to provide such duplicate cleaning elements is to prevent cross-contamination of ink colors. However, the use of multiple, substantially identical cleaning elements increases the cost and complexity of ink jet printers unnecessarily. Additionally, prior attempts at using a single cleaning element have resulted in cross contamination. This principle can be applied on broader basis to other types of ejection systems. Multiple ejectors ejecting fluids that should not be mixed can be cleaned using embodiments, as can a single ejector ejecting multiple fluids that should not be mixed. Embodiments employed in inkjet printers will be discussed for ease of description, but other types of ejectors can employ embodiments as well.
Some ink jet printer printheads that use water based inks, such as, for example, acoustic and thermal ink jet printheads, are difficult to clean. Ink jet printers that use such difficult-to-clean printheads employ cleaning systems that become soiled over time. These soiled cleaning systems typically must be replaced at regular intervals. Ink jet printers that use such difficult-to-clean printheads also typically use complex seal mechanisms at the printhead-cleaning system interface to prevent cleaning fluid from spilling or otherwise leaking at the interface.
Some cleaning systems use rotating cleaning rollers that dip into cleaning fluid contained in a cleaning chamber. In operation, a squeegee roller bears against the cleaning roller and squeezes out excess cleaning fluid. Then, a rotating cleaning roller bears against the printhead to apply cleaning fluid to the soiled printhead. The applied cleaning fluid dissolves and washes away dried ink, including dried ink plugs, paper dust and other printhead contaminants from the printhead orifices into the cleaning fluid in the cleaning chamber, where the dried ink and other contaminants are dissolved into the cleaning fluid contained in the cleaning chamber.
Problems with ink jet printhead cleaning systems include buildup of ink and/or other contaminants in the cleaning fluid with each cleaning cycle, and evaporation of water and other non-volatile liquids from the cleaning solutions during periods of non-use. These problems sharply reduce the useful life of cleaning fluids by increasing the concentration levels of ink in the cleaning fluid.
That is, the concentration ratio of ink to cleaning fluid in the cleaning fluid contained in the cleaning chamber increases as the cleaning fluid is used to clean the printhead. As a result, the cleaning fluid becomes less efficient at cleaning the printheads. After a certain number of cleaning cycles, the cleaning fluid resident in the cleaning chamber becomes too contaminated to effectively clean printheads.
Embodiments provide methods and systems that maintain the concentration of ink in the cleaning fluid throughout the life of the printer at levels where the effectiveness of the cleaning fluid in removing contaminants is not substantially impaired.
Embodiments separately provide systems and methods that compensate for and/or reduce the evaporation of volatile chemical compounds from the cleaning fluid.
Embodiments separately provide systems and methods that reduce the build-up of ink and/or other contaminants in the cleaning fluid.
In various exemplary embodiments, one or more of these features can be provided by, for example, pumping cleaning fluid into the printhead cleaning chamber only when one or more of the printheads need to be cleaned. After the printhead cleaning operation is completed, the cleaning fluid left in the cleaning chamber is removed from the cleaning chamber and sent to holding tanks. The holding tanks are closed containers in which the cleaning fluids are held to prevent evaporation of volatile materials in the cleaning fluid.
At various intervals, a known amount of contaminated cleaning fluid is removed from one or more of the holding tanks to a leach bed. The leach bed has a capacity to hold waste cleaning fluid bled to it from the holding tanks and is able to evaporate the waste cleaning fluid effectively over the life of the printer. A measured amount of fresh, i.e. uncontaminated, substitute cleaning fluid is then added into the one or more holding tanks from a corresponding cleaning fluid container. This results in maintaining the ink/cleaning fluid concentration in the holding tanks within ranges that result in effective long term cleaning of the printheads, for example, for the useful life of the printer. This can also compensate for any volatile compounds lost from the usable cleaning fluid due to evaporation.
In particular, embodiments employ a single cleaning roller to clean all printheads in an inkjet printer. This is achieved by allocating portions of the cleaning roller to each printhead. Similarly, embodiments can employ a single cleaning roller to clean ejectors that eject fluids that should not be mixed, even in the case where one ejector ejects multiple fluids that should not be mixed.
Embodiments employ a timing system that synchronizes the cleaning roller with the position of the printhead. The timing system ensures that the specific sections of the cleaning roller are properly aligned to selectively clean, for example, the C, M, Y and K printheads of an inkjet printer. This substantially reduces color mixing and cross-contamination of colors.
The main thrust of the invention is a scheme, whereby it is possible to use one “common” cleaning roller for the C, M, Y and K printheads. This is achieved by apportioning sections of the cleaning roller for a particular color printhead. This is done by synchronizing the rotary motion of the cleaning roll and the translatory motion of the printheads across the cleaning roll so that the same section of the cleaning roll is always in contact with a particular color printhead during the cleaning cycle. The action of the cleaning roll during the cleaning cycle is two-fold: dissolve the dried ink on the apertures as well as any debris/detritus during one half of the cleaning cycle and during the second half to transfer waste ink and other debris from the printhead to the cleaning solution in the cleaning chamber.
Synchronization of the cleaning roller rotary motion and the translatory motion of the printhead slide is accomplished by establishing a zero “start point” through the rotary encoder on the cleaning roller motor for the cleaning roller and a zero “start point” for the printhead slide through the linear encoder on the printhead slide.
A cheaper alternative might be a light interrupt sensor that senses a flag attached to a drive gear on the cleaner roll assembly.
While it is true that the cleaner roll transport waste inks of all colors into one common cleaning sump, the amount of waste ink per printhead is small on the order of 0.05 to 0.1 ml max per printhead per color in a cleaning sump fill with cleaning fluid (typically de-ionized water) with a capacity of 200-300 ml.
The concentration ratio of the ink/cleaning fluid is important. For effective cleaning, an ink/cleaning fluid ratio of no greater than 0.15 has been established. That means that if we take the 200 ml capacity conservative case, for instance, as much as 30 mls of waste ink of all colors can be dumped into the cleaning tank before the cleaning solution has to be replaced in toto. In other words, 150 to 300 cleaning cycles can be accomplished without having to change the cleaning solution.